1. Field of the Invention
This invention relates to apparatus for making slivers from a lap, comprising a plurality of tooth-carrying carding drums, which closely succeed each other in the direction of travel of the lap and which rotate in the same sense, wherein each carding drum which succeeds another in the direction of travel of the lap constitutes a worker roller for cooperating with the preceding carding drum, ejection ducts are provided, which extend from respective triangular spaces defined by adjacent carding drums and serve to conduct lap fibers which fly under centrifugal force from the carding drums, and an air-permeable collecting surface is provided, which is continuously moved and to which a vacuum is applied and which serves to receive the fibers from said ducts.
2. Description of the Prior Art
When rovings are to be made from a lap, the lap is initially carded by means of at least one tooth carrying carding drum and is subsequently divided into a plurality of slivers, which are then combined to form rovings. For this reason the uniformity of said rovings will depend on the uniformity of the slivers and the uniformity of the slivers will not be satisfactory when slivers are made at a high throughput rate.
It is known from Austrian Patent Specification No. 379,619 that in the making of a random-laid nonwoven web an excellent opening of the lap and a uniform deposition of the fibers on a collecting surface, to which a vacuum is applied, can be achieved in that a plurality of carding drums rotating in the same sense are arranged in close succession in such a manner that each carding drum which succeeds another constitutes a worker roller for combing the fibrous material that is being supplied by the preceding carding drum and those fibers which have not been combed out are thrown off below the carding drums onto the collecting surface immediately after the combing operation. As a result, the lap is divided into a plurality of partial streams of fibers, which are successively applied to the collecting surface and which may have a low fiber density even if the throughput rate of material through the apparatus is relatively high. Such a low fiber density and the application of the fibers in a plurality of layers are essential for the making of a highly uniform web.
From U.S. Pat. No. 2,274,425 it is also known that the coherence of the fibrous structure of rovings that have been made from a nonwoven web or from fibers which have been deposited on a conveyor belt after a free flight can be improved in that the conveyor belt which receives the fibers or the nonwoven web is provided with suction zones, which are inclined with respect to the direction of travel of the conveyor belt, and in that air is blown through the conveyor belt between said suction zones, so that fibers are blown off from and sucked onto the conveyor belt in respective zones and the fibers are thus divided into rovings. Owing to the inclination of the suction zones relative to the direction of conveyance of the conveyor belt said rovings are subjected to a transverse force and to a torque. Said torque is intended to consolidate the fibrous structure of each roving. That known apparatus had the disadvantage that the distribution of the fibers within the several rovings is subjected to substantial disturbing influences so that highly uniform rovings cannot be made. Besides, the throughput rate which can be achieved is limited.
To permit the making of drawn sliver having the high uniformity which is required for a subsequent spinning of drawn sliver, a plurality of slivers are supplied to a common drawing frame, in which a drawn sliver is formed from the individual slivers. That drawn sliver is then deposited by means of revolving disc into a can. Because the known apparatus for making slivers have a much higher throughput rate than drawing frames, the slivers must first be deposited in cans and must then be supplied to the drawing frame, in which a drawn sliver is made. When the supplies of sliver in the respective can have been consumed, the empty cans must be replaced by full cans so that the making of drawn sliver will have to be interrupted even if the replacement of cans is automatically performed. Besides, such automatic replacement involves a high structural expenditure.